There are five areas of technical background affecting this application: parking system management, radars, antennas, power management, and wireless communications protocols. Each area has technical problems discussed below.
Parking System Management:
Sensor-based parking detection systems are becoming increasingly popular, affordable and economical. These systems can determine when a vehicle enters a parking spot and when it leaves, but they cannot detect or identify a specific vehicle in a specific parking spot. However there are several potential applications that cannot be supported without knowing which vehicle is in which parking spot:                Parking tickets cannot automatically be generated for an unidentified vehicle illegally parked in a parking spot. Examples include                    a vehicle parked in a parking spot reserved for another,            a vehicle parked in a parking spot whose paid time has run out,            a vehicle parked in the parking spot without paying the parking fee and            a vehicle parked in a spot not designated for parking.                        Parking fees cannot be automatically requested for the time the unidentified vehicle spends parked in the parking spot.        Parking spot reservations cannot be confirmed without knowing the identity of the vehicle that is parked in the reserved parking spot.        
Most parking structures and parking areas have designated parking spots where drivers should park their vehicles. Often, vehicles are parked appropriately and with high efficiency, allowing the parking structure to be optimally used.                However, some vehicles may be parked incorrectly, often taking up more than one parking spot and/or sticking out into the parking traffic lane.        Taking up more than one parking spot lowers the efficiency of the parking facility, frustrating other drivers trying to park and lowering the revenue of the parking facility.        Vehicles sticking out into the parking traffic lane can lead to dangerous situations in which traffic accidents occur.        What is needed is an automated, reliable process that can note incorrectly parked vehicles and report these incorrectly parked vehicles to a parking management system and/or to a parking enforcement authority. The vehicle owner may be charged more and/or possibly issued a parking ticket.        
Regarding Radars:
There has been extensive development of radar since the 1930's for detecting aircraft and ships at a distance, often over the horizon. Such systems routinely use many kilowatts to megawatts for transmitting their radar pulses.                What is disclosed herein are micro-radars that use ten milli-Watts (mW) or less of power to transmit their pulses.        Micro-radars are used to detect vehicles and determine distances, where the distances involved are typically within a few meters of the micro-radar.        One of the technical problems with existing micro-radar technology has to do the difficulties calibrating and maintaining the calibration of a micro-radar unit.        In solving these problems, micro-radars can be inexpensively implemented and recalibrated throughout the life of a sensor without human intervention.        
Regarding Antennas:
There is extensive literature about microwave antennas.                However only a small fraction of that literature is relevant to applications involving a microwave antenna interacting with a transceiver whose active signals are in the range of less than 10 milli-watts. Such microwave antennas will be referred to as having a micro-power range compatible with the micro-radars of this disclosure.        These antennas are small antennas with a maximum physical dimension that is less than 7 centimeters (cm).        Microwave antennas tend to have a transmission and reception pattern. This pattern has lobes all around the antenna when plotted with the antenna at the center of the plane of maximum transmission power and receptivity.        Microwave antenna components were, and are, very poor at determining the location of an object, even to the point of knowing whether it is coming from the left or the right side of the antenna.        The way this problem was solved in large radars was with the use of a large array of antennas and/or a parabolic reflector, which changed the lobe pattern to one that dominated a half of the plane to indicate direction.        However, these approaches cannot be used in small, micro-power antenna applications. There is simply no room for such approaches.        Existing small, micro-power antennas cannot be used to detect which half of the plane an object is in. Put another way, they cannot detect whether a vehicle is parked to the left or the right of a micro-radar sensor. The sensor cannot tell which of two parking spots 20 is occupied.        
Regarding Power Management:
One common prior art configuration of remote power supplies includes one or more solar cells and rechargeable batteries.                Where there are significant periods of either massive cloud cover or very little daylight, solar cells may be unable to charge rechargeable batteries.        
Regarding Wireless Communications Protocols:
There are a number of wireless communication protocols, many of which have successfully implemented hand-off of a moving radio client or user within a cellular network from one base station to another.                In other applications, a sea of clients, in particular wireless sensors, may be fixed in location and wirelessly interface through repeaters to access points.        Allocating which wireless repeater passes on messages from which wireless sensor node to the access point can be solved with static allocation software, but at a steep price: These allocations may fail to respond to a changing wireless environment, such as the parking of a large truck or container between a wireless sensor and a repeater.        